Processing of color photographic materials



United States Patent 4 Claims. or. 9656) The invention relates to a method for processing color photographic materials, and more particularly, to a method for reducing fog formation in photographic images which have been color developed and treated with a bleach-fixing bath.

When producing color images by chromogenic development, it is necessary to remove the silver image which forms together with the dye image. For this purpose, the silver of the silver image must be oxidized and removed with a solvent for silver halide. This can be effected by treatment with a potassium ferricyanide bath and subsequently with a sodium thiosulphate bath. In order that the processing may be as simple as possible, attempts have been made to find bleach-fixing baths in which both steps take place at once. Such zleach-fixing baths are already known from German Patent No. 866,605. They contain sodium thiosulphate as solvent for silver halide and complexes of trivalent iron as oxidant for the metallic silver. The complex of ethylene diamine tetraacetic acid has proved particularly suitable, since it is a sufiiciently strong oxidizing agent to oxidize the silver image but is not so strong as to prevent the production of stable bleach-fixing baths.

The bleaching power of such a stable bleach-fixing bath is naturally considerably less than that of a potassium ferricyanide bleaching bath; this can satisfactorily be shown by measuring its redox potential. The redox potential is not, however, the only factor deciding the eflicacy of the bleach-fixing bath. The bleaching power and the fixing power of a bleach-fixing bath can, in fact, be improved considerably by additives which do not influence the redox potential of the bath, for example, by polyethylene oxides, according to British Patent No. 746,567 or by substances containing a thiocarbonyl C S) group, according to Swiss Patent No. 336,257.

It has long been known that bleach-fixing baths do not always lead to satisfactory bleaching of the silver image. Often the non-image areas (that is to say those areas of the color developed image which are devoid of image dye) display a grey to brownish coloring. The nature of this discoloration and the reasons for its formation are not clear.

The addition of iodide ions to the bleach-fixing bath to improve the discoloration is recommended in British Patent No. 926,569. Even though this step brings some improvement it is still not sufiicient. The discoloration is particularly disturbing with multi-layer color papers which are processed by the color reversal process.

It has now been found that color images, especially color reversal images of excellent quality are obtained if an intermediate treatment with a bath containing iodide ions is carried out between the color-forming development and the bleach-fixing. This intermediate bath can be an aqueous solution of a water-soluble iodide which solution may be adjusted to a pH value of2 to 9. When the solution has an acid pH value it serves at the same time to stop the color development. The solution may furthermore contain buffering agents, such as primary and secondary sodium phosphates.

In principle, it is only important that iodide ions be present in the intermediate bath. The concentration of iodides or iodide ions can be 0.01 to 10 grams and advantageously 0.5 to 1.5 grams per liter. All Water-soluble iodides are suitable, more especially alkali metal iodides, such as sodium or potassium iodides, as well as ammonium iodide, alkaline earth metal iodides, or iodides of primary, secondary or tertiary amines, or of quaternary organic ammonium bases, such as methyl amine, dicyclohexylamine, pyridine, morpholine, and tetramethylammonium base.

By these additions of iodide to the intermediate bath, a satisfactory bleaching and fixing of the color images in the bleaching and fixing bath is obtained, independent of the nature and composition of the bleach-fixing bath. The bleach-fixing bath may contain as fixing agent any water-soluble thiosulphate, such as sodium and ammonium thiosulphate.

Complex salts of trivalent iron (German Patent No. 866,605) or cobalt, as described, for example, in German Patent No. 954,475, preferably with hydroxypolycarboxylic and aminopolycarboxylic acids, are effective as bleaching agents. Complex salts of trivalent iron with aniinopolycar-boxylic acids such as with the following acids are particularly preferred.

Ethylenediaminetetraacetic acid;

Diethylene triaminepentaacetic acid;

Cyclohexane-1,2-diaminetetraacetic acid;

Nitrilo-triacetic acid;

N(CH COOH) Ethylaminedipropionic acid [:bis- (Z-carb oxyethyl) ethylamine] H C N (CH CH COOH) 2 The color photographic materials used in the present invention comprise silver halide emulsion layers which contain color couplers capable of reacting with the oxidation products of primary aromatic amino developing agents to form dyestuff images. Such materials usually contain in superirnposedrelationship three silver halide emulsion layers which are sensitized to different regions of the spectrum and which contain couplers for the production of yellow, magenta and cyan dyestuif images.

Example A normal commercial Agfacolor reversal paper is exposed behind a stepped wedge and subjected to reversal development. The first development is etfected in a blackand-white developer solution containing per one liter 6 grams of hydroquinone, 0.5 gram of 1-phenyl-3-pyrazolidone, 20 grams of sodium sulfite, 50 grams of soda, and 2 grams of potassium bromide (developing time minutes); the color development, after the second exposure, is carried out for minutes with a developer solution containing per one liter 2.5 grams of N,'N-diethyl-p-phenylene diamine sulphate, 5 grams of sodium sulfite, 75 grams of potassium carbonate, 2 grams of potassium bromide, 1.5 grams of hydroxylamine hydrochloride. The reversal paper is now cut into 4 strips, which are further processed in different ways.

A The first strip is treated for 3 minutes in an intermediate bath having the following composition:

30 grams of sodium acetate 5 ml. of glacial acetic acid 1 gram of potassium iodide 1000 ml. of water.

The pH is 5.2. The image silver is thereafter removed by a bleachfixing bath with the following composition:

40 grams of the sodium salt of the iron complex of ethylene diamine tetraacetic acid,

3.78 grams of free ethylene diamine tetraacetic acid,

10 grams of anhydrous sodium sulphite,

200 grams of crystalline sodium thiosulphate, made up with Water to 1 liter.

The pH is 6.2.

B A second strip is treated with an intermediate bath which differs from that used for strip A in containing no potassium iodide; the further processing takes place as with the strip A C The third strip, after treatment with the iodidefree intermediate bath of strip B is processed in the previously described bleach-fixing bath, which additionally contains 1 g. of potassium iodide. This procedure corresponds to that described in British Patent No. 926,- 569.

D The fourth strip is processed in the intermediate bath of strip A and the bleach-fixing bath of strip C The images obtained by these processes show the following results as regards their image whites:

The quality of the colors of the strip A is superior to the other three test images. The worst result was produced by the processing method B The addition of iodide to the bleach-fixing bath (strip C according to British Patent No. 926,569, undoubtedly provides some improvement, but is clearly inferior to the process according to the invention, (strip A The addition of iodide to the intermediate bath and to the bleach-fixing bath (strip D produces no improvement by comparison with strip A The fogging densities in the image whites were measured with a densitometer by means of blue light and the following data were'obtained.

The same series of experiments was repeated, but using an intermediate bath having the following composition, and a pH of 7.0:

Grams NaH PO NfigHPOg Sodium hexametaphosphate 1 Water to make one liter.

The following processing procedure is employed in this series of experiments:

A The intermediate bath described above and having a pH of 7.0 contains also 1 gram of potassium iodide per liter; bleach-fixing bath as described above, containing no iodide.

B Intermediate bath and bleach-fixing bath without iodide.

C Intermediate bath without iodide, bleach-fixing bath with iodide.

D Intermediate bath and bleach-fixing bath with iodide.

The fogging densities in the image whites (measured with blue light) are set out in the following table.

Specimen: Fogging density A, 0.14 B 0.33 C 0.23 D 0.15

The experiments A and A were repeated again, and

with three different batches in each case, intermediate.

rinses of respectively 5 minutes, 30 minutes and 24 hours duration being carried out between the treatment with the iodide-containing intermediate bath and the iodidefree bleach-fixing bath. In all experiments, the same fogging densities of the image Whites were measured, within the limits of error, as in the experiments A and A in which there was no rinsing. It must be concluded from these experiments that, in the process according to the invention, there is not a simple entrainment of iodideinto the bleach-fixing bath by a pretreatment with an iodide-containing bath, but that, surprisingly, a reaction takes place with the iodide-containing intermediate bath, which fixes the iodide, so that the effect of these iodide ions, which only becomes operative in the bleach-fixing bath, is not prevented by an intense intermediate rinsing lasting 24 hours.

The present invention is primarily concerned with such materials which are intended for reversal processes, wherein the irnagewise exposed material is given a conventional black and white development, followed by a reversal exposure, and color-forming development. However, the process of. the present invention may also be applied for the production of color images by the negative-positive process wherein the materials are color developed after imagewise exposure. The invention is of primary importance for the processing of multi-layer materials which have a paper support and which are intended for the production of color photographic printing especially reversal prints- What is claimed is:

1. In a process for the production of photographic color images which comprises the steps of 1) imagewrse exposing a photographic material comprising at least one silver halide emulsion layer which contains a color coupler capable of reacting with the oxidation product of a color-forming developer to form a dye; (2) developing the said material to form a silver and a color image, and (3) thereafter treating the said material with an aqueous bath containing botha silver halide solvent and a silver bleaching agent, the improvement which comprises subjecting the said material between said steps 2 and 3 to an aqueous solution containing iodide ions.

2. In a process for the production of photographic color reversal images which comprises the steps of (1) imagewise exposing a photographic material comprising at least one silver halide emulsion layer which contains a color coupler capable of reacting with the oxidation product of a color-forming .developer to form a dye; (2) developing the said material in a black and White developer solution to form at the exposed areas of said material a silver image, (3) exposing the said material, (4) developing the said material to form a silver and a dye image at the areas which are not exposed by step (1), (5) thereafter treating the said material with an aqueous bath containing both a silver halide solvent and 5 6 a silver bleaching agent, the improvement which comprises References Cited subjlecting the sfaid material lbetween said steps 4 and 5 UNITED STATES PATENTS to t e action 0 an aqueous ath containing iodide ions.

3. The combination of claim 1 in which the aqueous gg? 5 I 96*62 solution containing the iodide ions is a short stop bath 5 9 1/1 unt er et 96*62 and the iodide ion concentration is from about 0 5 to 2827375 3/1958 Andreyev 9662 3,210,189 10/1965 Wartburg 96-62 about 1.5 grams per liter.

4. The combination of claim 2 in which the aqueous FOREIGN PATENTS solution containing the iodide ions is a short stop bath 1,284,492 1/1962 France and the iodide ion concentration is from about 0.5 to 10 about 1.5 grams per liter. J. TRAVIS BROWN, Primary Examiner. 

1. IN A PROCESS FOR THE PRODUCTION OF PHOTOGRAPHIC COLOR IMAGES WHICH COMPRISES THE STEPS OF (1) IMAGEWISE EXPOSING A PHOTOGRAPHIC MATERIAL COMPRISING AT LEAST ONE SILVER HALIDE EMULSION LAYER WHICH CONTAINS A COLOR COUPLER CAPABLE OF REACTING WITH THE OXIDATION PRODUCT OF A COLOR-FORMING DEVELOPER TO FORM A DYE; (2) DEVELOPING THE SAID MATERIAL TO FORM A SILVER AND A COLOR IMAGE, AND (3) THEREAFTER TREATING THE SAID MATERIAL WITH AN AQUEOUS BATH CONTAINING BOTH A SILVER HALIDE SOLVENT AND A SILVER BLEACHING AGENT, THE IMPROVEMENT WHICH COMPRISES SUBJECTING THE SAID MATERIAL BETWEEN SAID STEPS 2 AND 3 TO AN AQUEOUS SOLUTION CONTAINING IODIDE IONS. 